The present invention relates to a pressure sensitive switch, and more particularly to a mattress-switch for use in a bed egress alarm system. Such systems are typically employed in hospitals to continuously monitor the presence of a patient in a bed and to alert the hospital staff when a patient departs from the bed. A pressure-sensitive switch is typically inserted under the mattress, preferably closing an electrical alarm circuit under the weight of the patient on the mattress and opening the circuit to actuate the alarm when the patient departs. It is preferred that the switch be designed to open, rather than to close, upon departure of a person from the mattress, so that the more likely fail-open condition will always be called to the attention of the staff.
Pressure switches of the prior art, that are suitable for such use, employ a pair of metal strips, plates, sheets or wire mesh screening, the two metal members being separated by one or more insulative members such that physical distortion or compression of the assembly causes contact between the two metal pieces.
The pressure necessary to close such switches and/or the pressure at which the switch opens after having been pressed closed, tends to change with long periods of use and the degree of such sensitivity changes is a function of the loads to which it has been exposed. Such changes in sensitivity are most prominently due to the metal members taking a permanent set while being distorted or compressed.
It is an object of the present invention to overcome the shortcomings of such prior art switches.
It is a further object of this invention to provide a mattress-switch for use in a bed egress alarm system that is reliably operable for alternately detecting the presence in and absence from the bed of persons of widely different weights.